Transport and metabolism of the tea flavonoid (-)-epicatechin by the humanintestinal cell line Caco-2

Purpose: Tea flavonoids, including (-)-epicatechin (EC), have been suggeste d to have chemopreventive properties in cancer. However, there is limited k nowledge of the oral bioavailability of these dietary compounds. The purpos e of this study was to gain a better understanding of the absorption of EC. Methods: The intestinal epithelial membrane transport of EC was examined us ing the monolayer of the human Caco-2 cell line grown in Transwells, a comm on model of intestinal absorption. EC and its metabolites were measured by high performance liquid chromatography with diode array detection. Results: EC showed no apical to basolateral absorption at concentrations ra nging from 5 to 50 muM. In contrast, EC demonstrated basolateral to apical efflux with a P-app value of 0.67 +/- 0.05 x 10(-6) cm/sec, i.e., slightly higher than for mannitol, 0.50 +/- 0.30 x 10(-6) cm/ see, a paracellular tr ansport marker. There was a 50% reduction in the efflux of EC in the presen ce of 50 muM MK-571, a competitive inhibitor of the MRP2 transporter expres sed in the apical membrane of Caco-2 cells. Most important, the presence of 50 muM MK-571 resulted in clearly measurable apical to basolateral absorpt ion of EC with a P-app of 0.31 +/- 0.06 x 10-6 cm/sec. Two polar metabolite s, M1 and M2, were formed from EC, both of which appeared exclusively on th e apical side. MK-571 (50 muM) dramatically inhibited the transport for bot h of these metabolites. Incubations with inorganic (SO42-)-S-35 and hydroly sis by aryl sulfatase strongly suggested that these metabolites were sulfat e conjugates. Conclusions: These results suggest an important role for the multispecific organic anion transporter MRP2 in the bioavailability of EC and possibly ot her tea flavonoids.